Laser shock peening (LSP) is a new technology for strengthening material surface using intense shock wave induced by high-power pulsed laser, which has four distinct characteristics of high pressure, high energy, ultra-fast and ultra-high strain rate. The compressive residual stress produced by LSP can effectively eliminate stress concentration, and restrain crack initiation and growth in the surface layer of metallic components. It further remarkably improves the fatigue life, corrosion and wear resistance of the metallic components. Many researches showed that LSP is an effective method to prolong the time of crack initiation, reduce the crack growth speed and improve the fatigue life of components.
Surface morphology and surface roughness have a significant effect on the quality and property of metallic components, which directly affect the contact strength, corrosion resistance, wear resistance, fatigue resistance and sealing performance.
Due to the plastic deformation produced by LSP, micro-indentions occur in the surface. The spot edge is easy to bulge because of boundary effect. Hence the initiation and growth of fatigue cracks occur with both the increasing of the surface roughness and the formation of stress concentration. In practice, overlapping round spots are applied to strengthen the surface with a large area, which brings higher surface roughness and stress concentration. Moreover, this process further leads to the non-uniform distribution of residual stress on the surface of metallic component, and the inconsistent in the depth direction. As a result, fatigue failure of metallic components occurs.